CHAPTER H4 – Bovine Hyperekplexia

Inherited congenital myoclonus (ICM) is an autosomal recessive disease in Poll Hereford cattle and a model of human hyperekplexia or startle disease. It is characterized by spontaneous and stimulus-responsive myoclonic spasms that resemble tetany. High velocity muscle tremors can occasionally be detected as an audible hum. Cranial nerve functions are unimpaired. Reduction in glycine receptor expression levels explains the ICM phenotype, which provides additional information on the consequences of glycine receptor dysfunction. This chapter discusses the major clinical features of bovine hyperekplexia—ICM. ICM, a bovine model of human hyperekplexia, is considered as the most common inherited disease of newborn calves in Australia. Clinical findings of prenatal stimulus responsive myoclonic jerks and severe tetanic spasms characteristic of ICM were the result of a failure of glycine mediated inhibitory neurotransmission, as demonstrated by the loss of [ 3 H] strychnine binding sites from brainstem and spinal cord extracts in affected calves. Definition of the clinical, pathological, biochemical, and molecular aspects of ICM is the result of breeding experiments and laboratory studies involving many disciplines. The result is the characterization of a recessive inherited neurological disorder in cattle that provides a model for investigating the role of neurotransmitter receptors.